This invention relates to multilayer light-reflecting optical bodies. In addition, the invention relates to multilayer optical bodies that reflect light over a range of wavelengths (e.g., mirrors, color mirrored films, IR reflective films, and UV reflective films).
Polymeric films are used in a wide variety of applications. One particular use of polymeric films is in mirrors which reflect light over a particular wavelength range. Such reflective films can be disposed, for example, behind a backlight in liquid crystal displays to reflect light toward the display to enhance brightness of the display. Color shifting films can be used in signage, packaging materials, etc. IR mirror films can be used, for example, to reduce solar heat load entering a building or vehicle through its windows. Ultraviolet (UV) films can be used to protect other films or objects from UV light to prevent deleterious effects (e.g., photodegradation of a polymeric film).
Coextrusion casting processes have been used to make multilayer optical mirrors. Generally, however, cast films have a number of practical drawbacks. For example, cast films generally have low refractive index differences between the high and low index materials and do not generally have matching refractive indices in the z-direction, limiting the optical performance for a given number of layers. Because of the limited optical power of such cast films, dyes and pigments also typically are used to enhance the color of color mirror films. Moreover, some cast films, particularly films made of noncrystalline materials, can also have limited thermal stability, dimensional stability, environmental stability and/or solvent resistance.
Coextrusion-orientation processes have been used to provide films with better optical performance due to the large refractive index difference between high and low index materials and the capability of matching refractive indices in the z-, or out-of-plane direction when at least one of the materials is birefringent. One example of a previously formed film has high index layers formed of polyethylene naphthalate (PEN) and low index layers of polymethyl methacrylate (PMMA). Orientation of PEN increases the refractive indices of the PEN layers and, therefore, increases the optical power of the PEN/PMMA films. PEN, however, is a relatively expensive material which is difficult to protect from ultraviolet radiation, and polyethylene terephthalate (PET), a lower index alternative to PEN, cannot easily be suitably oriented with PMMA due to the difference in glass transition temperatures of these materials (about 84xc2x0 C. for PET and about 106xc2x0 C. for PMMA).
In aspect, the present invention provides an optical body, comprising: (a) a plurality of first optical layers, each first optical layer being oriented and comprising a polyester having terephthalate comonomer units and ethylene glycol comonomer units and having a glass transition temperature less than or equal to about 90xc2x0 C.; and (b) a plurality of second optical layers disposed in a repeating sequence with the plurality of first optical layers, each second optical layer comprising a polymer composition; the optical body being configured and arranged to reflect at least a portion of light over at least one wavelength region.
In another aspect, the invention provide an optical body, comprising: a plurality of first optical layers, each first optical layer being oriented and comprising a first polymer composition, the first polymer composition comprising:
(i) a polyester portion having terephthalate comonomer units and ethylene glycol comonomer units, and
(ii) a second portion corresponding to a polymer having a glass transition temperature of at least about 130xc2x0 C.; and
a plurality of second optical layers disposed in a repeating sequence with the plurality of first optical layers, each second optical layer comprising a second polymer composition.
In yet another aspect, the invention provides an optical body, comprising:
(i) a plurality of first optical layers, each first optical layer being oriented and comprising a polyester having terephthalate comonomer units and ethylene glycol comonomer units; and
(ii) a plurality of second optical layers disposed in a repeating sequence with the plurality of first optical layers, each second optical layer comprising a polymer composition, the polymer composition having a glass transition temperature of less than or equal to about 90xc2x0 C. and comprising a polymer selected from the group consisting of polyacrylates and aliphatic polyolefins.
In still another aspect, the invention provides an optical body, comprising: (a) a plurality of first optical layers, each first optical layer being oriented; and (b) a plurality of second optical layers disposed in a repeating sequence with the plurality of first optical layers, each second optical layer comprising a blend of polymethylmethacrylate and polyvinylidene fluoride; the optical body being configured and arranged to reflect at least a portion of light over at least one wavelength region.
Methods of making the above-described optical bodies, and articles employing such optical bodies are also provided.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.